@article{zhong_kirmani_lan_carpenter_rong-hui chew_awartani_yu_niazi_voznyy_hu_et al._2022, title={Conjugated polymers with controllable interfacial order and energetics enable tunable heterojunctions in organic and colloidal quantum dot photovoltaics}, volume={10}, ISSN={2050-7488 2050-7496}, url={http://dx.doi.org/10.1039/D1TA09544G}, DOI={10.1039/d1ta09544g}, abstractNote={Top and bottom surfaces of polymer films are used to construct interfaces in heterojunction based devices, affecting device figure of merit significantly with their different aggregation states.}, number={4}, journal={Journal of Materials Chemistry A}, publisher={Royal Society of Chemistry (RSC)}, author={Zhong, Yufei and Kirmani, Ahmad R. and Lan, Xinzheng and Carpenter, Joshua and Rong-Hui Chew, Annabel and Awartani, Omar and Yu, Liyang and Niazi, Muhammad R. and Voznyy, Oleksandr and Hu, Hanlin and et al.}, year={2022}, pages={1788–1801} }
 @article{carpenter_ghasemi_gann_angunawela_stuard_rech_ritchie_brendan t. o'connor_atkin_you_et al._2019, title={Competition between Exceptionally Long-Range Alkyl Sidechain Ordering and Backbone Ordering in Semiconducting Polymers and Its Impact on Electronic and Optoelectronic Properties}, volume={29}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201806977}, abstractNote={Abstract Intra‐ and intermolecular ordering greatly impacts the electronic and optoelectronic properties of semiconducting polymers. The interrelationship between ordering of alkyl sidechains and conjugated backbones has yet to be fully detailed, despite much prior effort. Here, the discovery of a highly ordered alkyl sidechain phase in six representative semiconducting polymers, determined from distinct spectroscopic and diffraction signatures, is reported. The sidechain ordering exhibits unusually large coherence lengths (≥70 nm), induces torsional/twisting backbone disorder, and results in a vertically multilayered nanostructure with ordered sidechain layers alternating with disordered backbone layers. Calorimetry and in situ variable temperature scattering measurements in a model system poly{4‐(5‐(4,8‐bis(3‐butylnonyl)‐6‐methylbenzo[1,2‐b:4,5‐b′]dithiophen‐2‐yl)thiophen‐2‐yl)‐2‐(2‐butyloctyl)‐5,6‐difluoro‐7‐(5‐methylthiophen‐2‐yl)‐2H‐benzo[d][1,2,3]triazole} (PBnDT‐FTAZ) clearly delineate this competition of ordering that prevents simultaneous long‐range order of both moieties. The long‐range sidechain ordering can be exploited as a transient state to fabricate PBnDT‐FTAZ films with an atypical edge‐on texture and 2.5× improved field‐effect transistor mobility. The observed influence of ordering between the moieties implies that improved molecular design can produce synergistic rather than destructive ordering effects. Given the large sidechain coherence lengths observed, such synergistic ordering should greatly improve the coherence length of backbone ordering and thereby improve electronic and optoelectronic properties such as charge transport and exciton diffusion lengths.}, number={5}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Carpenter, Joshua H. and Ghasemi, Masoud and Gann, Eliot and Angunawela, Indunil and Stuard, Samuel J. and Rech, Jeromy James and Ritchie, Earl and Brendan T. O'Connor and Atkin, Joanna and You, Wei and et al.}, year={2019}, month={Feb} }
 @article{ghasemi_hu_peng_rech_angunawela_carpenter_stuard_wadsworth_mcculloch_you_et al._2019, title={Delineation of Thermodynamic and Kinetic Factors that Control Stability in Non-fullerene Organic Solar Cells}, volume={3}, ISSN={["2542-4351"]}, DOI={10.1016/j.joule.2019.03.020}, abstractNote={•NF-OSCs with optimal miscibility are intrinsically stable against demixing•Crystallization of NF-SMA needs to be suppressed through proper vitrification•Polymers and NF-SMA with high Tg are needed to achieve long-term OSCs stability In recent years, the performance of organic solar cells (OSCs) has greatly improved with the development of novel non-fullerene small molecular acceptors (NF-SMA). The rapid increase in power conversion efficiency, now surpassing 15%, highlights an immediate and increasing need to understand the longevity and lifetime of NF-OSCs. However, the field relies mainly on a laborious trial-and-error approach to select polymer:NF-SMA pairs with desirable device stability. Here, we provide a structure-property relation that explains the morphological stability and burn-in degradation due to excessive demixing or crystallization. The framework presented in our study shows that a specific balance of interactions between polymer and NF-SMA can offer a short-term solution against excessive demixing. Long-term morphological stability that also suppresses crystallization can only be achieved by freezing in the initial quenched morphology through the use of polymers and/or NF-SMAs with low flexibility. Although non-fullerene small molecular acceptors (NF-SMAs) are dominating current research in organic solar cells (OSCs), measurements of thermodynamics drivers and kinetic factors determining their morphological stability are lacking. Here, we delineate and measure such factors in crystallizable NF-SMA blends and discuss four model systems with respect to their meta-stability and degree of vitrification. We determine for the first time the amorphous-amorphous phase diagram in an NF-SMA system and show that its deep quench depth can result in severe burn-in degradation. We estimate the relative phase behavior of four other materials systems. Additionally, we derive room-temperature diffusion coefficients and conclude that the morphology needs to be stabilized by vitrification corresponding to diffusion constants below 10−22 cm2/s. Our results show that to achieve stability via rational molecular design, the thermodynamics, glass transition temperature, diffusion properties, and related structure-function relations need to be more extensively studied and understood. Although non-fullerene small molecular acceptors (NF-SMAs) are dominating current research in organic solar cells (OSCs), measurements of thermodynamics drivers and kinetic factors determining their morphological stability are lacking. Here, we delineate and measure such factors in crystallizable NF-SMA blends and discuss four model systems with respect to their meta-stability and degree of vitrification. We determine for the first time the amorphous-amorphous phase diagram in an NF-SMA system and show that its deep quench depth can result in severe burn-in degradation. We estimate the relative phase behavior of four other materials systems. Additionally, we derive room-temperature diffusion coefficients and conclude that the morphology needs to be stabilized by vitrification corresponding to diffusion constants below 10−22 cm2/s. Our results show that to achieve stability via rational molecular design, the thermodynamics, glass transition temperature, diffusion properties, and related structure-function relations need to be more extensively studied and understood. The performance of solution-processed organic solar cells (OSCs) based on bulk heterojunction (BHJ) blends of a pair of donor and acceptor materials has greatly improved with the development of novel non-fullerene small molecular acceptors (NF-SMA).1Yan C. Barlow S. Wang Z. Yan H. Jen A.K.-Y. Marder S.R. Zhan X. Non-fullerene acceptors for organic solar cells.Nat. Rev. Mater. 2018; 3: 18003Crossref Scopus (1785) Google Scholar, 2Zhang G. Zhao J. Chow P.C.Y. Jiang K. Zhang J. Zhu Z. Zhang J. Huang F. Yan H. Nonfullerene acceptor molecules for bulk heterojunction organic solar cells.Chem. Rev. 2018; 118: 3447-3507Crossref PubMed Scopus (1160) Google Scholar, 3Li S. Liu W. Li C.Z. Shi M. Chen H. Efficient organic solar cells with non-fullerene acceptors.Small. 2017; 13: 1701120Crossref Scopus (200) Google Scholar, 4Nielsen C.B. Holliday S. Chen H.Y. Cryer S.J. McCulloch I. Non-fullerene electron acceptors for use in organic solar cells.Acc. Chem. Res. 2015; 48: 2803-2812Crossref PubMed Scopus (991) Google Scholar, 5Lin Y. Wang J. Zhang Z.G. Bai H. Li Y. Zhu D. Zhan X. An electron acceptor challenging fullerenes for efficient polymer solar cells.Adv. Mater. 2015; 27: 1170-1174Crossref PubMed Scopus (2812) Google Scholar With the power conversion efficiency (PCE) now reaching 12%–14% in many single-layer research devices,6Fei Z. Eisner F.D. Jiao X. Azzouzi M. Röhr J.A. Han Y. Shahid M. Chesman A.S.R. Easton C.D. McNeill C.R. et al.An alkylated indacenodithieno[3,2-b]thiophene-based nonfullerene acceptor with high crystallinity exhibiting single junction solar cell efficiencies greater than 13% with low voltage losses.Adv. Mater. 2018; 30: 1705209Crossref Scopus (434) Google Scholar, 7Li S. Ye L. Zhao W. Yan H. Yang B. Liu D. Li W. Ade H. Hou J. A wide band gap polymer with a deep highest occupied molecular orbital level enables 14.2% efficiency in polymer solar cells.J. Am. Chem. Soc. 2018; 140: 7159-7167Crossref PubMed Scopus (600) Google Scholar, 8Luo Z. Bin H. Liu T. Zhang Z.G. Yang Y. Zhong C. Qiu B. Li G. Gao W. Xie D. et al.Fine-tuning of molecular packing and energy level through methyl substitution enabling excellent small molecule acceptors for nonfullerene polymer solar cells with efficiency up to 12.54%.Adv. Mater. 2018; 30: 1706124Crossref Scopus (253) Google Scholar, 9Li T. Dai S. Ke Z. Yang L. Wang J. Yan C. Ma W. Zhan X. Fused tris(thienothiophene)-based electron acceptor with strong near-infrared absorption for high-performance as-cast solar cells.Adv. Mater. 2018; 30: 1705969Crossref Scopus (320) Google Scholar, 10Sun C. Pan F. Bin H. Zhang J. Xue L. Qiu B. Wei Z. Zhang Z.G. Li Y. A low cost and high performance polymer donor material for polymer solar cells.Nat. Commun. 2018; 9: 743Crossref PubMed Scopus (523) Google Scholar, 11Liu W. Zhang J. Zhou Z. Zhang D. Zhang Y. Xu S. Zhu X. Design of a new fused-ring electron acceptor with excellent compatibility to wide-bandgap polymer donors for high-performance organic photovoltaics.Adv. Mater. 2018; 30: 1800403Crossref Scopus (167) Google Scholar, 12Xu X. Yu T. Bi Z. Ma W. Li Y. Peng Q. Realizing over 13% efficiency in green-solvent-processed nonfullerene organic solar cells enabled by 1,3,4-thiadiazole-based wide-bandgap copolymers.Adv. Mater. 2017; 29: 1703973Google Scholar, 13Kan B. Zhang J. Liu F. Wan X. Li C. Ke X. Wang Y. Feng H. Zhang Y. Long G. et al.Fine-tuning the energy levels of a nonfullerene small-molecule acceptor to achieve a high short-circuit current and a power conversion efficiency over 12% in organic solar cells.Adv. Mater. 2017; 29: 1704904Google Scholar, 14Ye L. Zhao W. Li S. Mukherjee S. Carpenter J.H. Awartani O. Jiao X. Hou J. Ade H. High-efficiency nonfullerene organic solar cells: critical factors that affect complex multi-length scale morphology and device performance.Adv. Energy Mater. 2016; 6: 1602000Google Scholar the principles governing operational stability are becoming very important and need to be understood.15de Zerio A.D. Müller C. Glass forming acceptor alloys for highly efficient and thermally stable ternary organic solar cells.Adv. Energy Mater. 2018; 8: 1702741Crossref Scopus (69) Google Scholar, 16Baran D. Ashraf R.S. Hanifi D.A. Abdelsamie M. Gasparini N. Röhr J.A. Holliday S. Wadsworth A. Lockett S. Neophytou M. et al.Reducing the efficiency-stability-cost gap of organic photovoltaics with highly efficient and stable small molecule acceptor ternary solar cells.Nat. Mater. 2017; 16: 363-369Crossref PubMed Scopus (842) Google Scholar, 17Cheng P. Zhan X. Stability of organic solar cells: challenges and strategies.Chem. Soc. Rev. 2016; 45: 2544-2582Crossref PubMed Google Scholar, 18Jørgensen M. Norrman K. Gevorgyan S.A. Tromholt T. Andreasen B. Krebs F.C. Stability of polymer solar cells.Adv. Mater. 2012; 24: 580-612Crossref PubMed Scopus (1208) Google Scholar, 19Baran D. Gasparini N. Wadsworth A. Tan C.H. Wehbe N. Song X. Hamid Z. Zhang W. Neophytou M. Kirchartz T. et al.Robust nonfullerene solar cells approaching unity external quantum efficiency enabled by suppression of geminate recombination.Nat. Commun. 2018; 9: 2059Crossref PubMed Scopus (134) Google Scholar The lifetime of an OSC can be limited by various factors, such as exposure to humidity,20Klumbies H. Karl M. Hermenau M. Rösch R. Seeland M. Hoppe H. Müller-Meskamp L. Leo K. Water ingress into and climate dependent lifetime of organic photovoltaic cells investigated by calcium corrosion tests.Sol. Energy Mater. Sol. Cells. 2014; 120: 685-690Crossref Scopus (46) Google Scholar photo-oxidation of the BHJ layer,21Reese M.O. Nardes A.M. Rupert B.L. Larsen R.E. Olsen D.C. Lloyd M.T. Shaheen S.E. Ginley E.S. Rumbles G. Kopidakis N. Photoinduced degradation of polymer and polymer–fullerene active layers: experiment and theory.Adv. Funct. Mater. 2014; 20: 3476-3483Crossref Scopus (246) Google Scholar and morphological instability due to diffusion or aggregation and, crystallization even at room temperature (RT).22Li N. Perea J.D. Kassar T. Richter M. Heumueller T. Matt G.J. Hou Y. Güldal N.S. Chen H. Chen S. et al.Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing.Nat. Commun. 2017; 8: 14541Crossref PubMed Scopus (263) Google Scholar Because of the dominance of fullerenes as acceptors for more than two decades,23Yu G. Gao J. Hummelen J.C. Wudl F. Heeger A.J. Polymer photovoltaic cells - enhanced efficiencies via a network of internal donor-acceptor heterojunctions.Science. 1995; 270: 1789-1791Crossref Scopus (9682) Google Scholar, 24Thompson B.C. Fréchet J.M. Polymer-fullerene composite solar cells.Angew. Chem. Int. Ed. Engl. 2008; 47: 58-77Crossref PubMed Scopus (3851) Google Scholar, 25Dou L. You J. Hong Z. Xu Z. Li G. Street R.A. Yang Y. 25th anniversary article: a decade of organic/polymeric photovoltaic research.Adv. Mater. 2013; 25: 6642-6671Crossref PubMed Scopus (1032) Google Scholar, 26Hu H. Chow P.C.Y. Zhang G. Ma T. Liu J. Yang G. Yan H. Design of donor polymers with strong temperature-dependent aggregation property for efficient organic photovoltaics.Acc. Chem. Res. 2017; 50: 2519-2528Crossref PubMed Scopus (186) Google Scholar it is not surprising that most stability investigations to date have been focusing on fullerene-based OSCs. Given the clear difference in the molecular structure and size of the non-fullerene and fullerene acceptors, the chemical and morphological stability of the NF-SMA OSCs cannot be extrapolated from data on fullerene devices. The stability of NF-SMA OSCs and, importantly, its thermodynamic drivers and mechanical or thermal factors that relate to vitrification, remain largely unexplored. To rationally enhance the operational lifetime of NF-SMA-based OSCs, the factors that control the morphological stability of the active layer need to be investigated and understood in depth. An efficiency loss in the first few hundred hours of the operation of an unstable OSC is generally referred to as “burn-in” and can be caused by various factors such as trap state formation,27Peters C.H. Sachs-Quintana I.T. Mateker W.R. Heumueller T. Rivnay J. Noriega R. Beiley Z.M. Hoke E.T. Salleo A. McGehee M.D. The mechanism of burn-in loss in a high efficiency polymer solar cell.Adv. Mater. 2012; 24: 663-668Crossref PubMed Scopus (217) Google Scholar photo-oxidation and oligomerization,28Burlingame Q. Tong X. Hankett J. Slootsky M. Chen Z. Forrest S.R. Photochemical origins of burn-in degradation in small molecular weight organic photovoltaic cells.Energy Environ. Sci. 2015; 8: 1005-1010Crossref Google Scholar degradation of interlayers,29Kam Z. Wang X. Zhang J. Wu J. Elimination of burn-in open-circuit voltage degradation by ZnO surface modification in organic solar cells.ACS Appl. Mater. Interfaces. 2015; 7: 1608-1615Crossref PubMed Scopus (44) Google Scholar and over-purification of the mixed domains.22Li N. Perea J.D. Kassar T. Richter M. Heumueller T. Matt G.J. Hou Y. Güldal N.S. Chen H. Chen S. et al.Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing.Nat. Commun. 2017; 8: 14541Crossref PubMed Scopus (263) Google Scholar Among these factors, we focus on the impact of morphological instabilities and refer to the impact on device degradation simply as “burn-in” hereafter, mindful that other factors can in principle also cause burn-in. Burn-in driven by over-purification of mixed domains and/or crystallization have been extensively studied and linked to morphological instability in fullerene-based systems,22Li N. Perea J.D. Kassar T. Richter M. Heumueller T. Matt G.J. Hou Y. Güldal N.S. Chen H. Chen S. et al.Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing.Nat. Commun. 2017; 8: 14541Crossref PubMed Scopus (263) Google Scholar, 30Mendaza A.D. Melianas A. Rossbauer S. Bäcke O. Nordstierna L. Erhart P. Olsson E. Anthopoulos T.D. Inganäs O. Müller C. High-entropy mixtures of pristine fullerenes for solution-processed transistors and solar cells.Adv. Mater. 2015; 27: 7325-7331Crossref PubMed Scopus (45) Google Scholar, 31Lindqvist C. Bergqvist J. Bäcke O. Gustafsson S. Wang E. Olsson E. Inganäs O. Andersson M.R. Müller C. Fullerene mixtures enhance the thermal stability of a non-crystalline polymer solar cell blend.Appl. Phys. Lett. 2014; 104: 153301Crossref Scopus (43) Google Scholar, 32Schroeder B.C. Li Z. Brady M.A. Faria G.C. Ashraf R.S. Takacs C.J. Cowart J.S. Duong D.T. Chiu K.H. Tan C.H. et al.Enhancing fullerene-based solar cell lifetimes by addition of a fullerene dumbbell.Angew. Chem. Int. Ed. Engl. 2014; 53: 12870-12875Crossref PubMed Scopus (79) Google Scholar but these two main morphological instabilities have just started to be investigated for NF-SMA-based devices, primarily in a phenomenological manner without elucidating thermodynamics drivers and kinetic factors and their relation to molecular design.33Cha H. Wu J. Wadsworth A. Nagitta J. Limbu S. Pont S. Li Z. Searle J. Wyatt M.F. Baran D. et al.An efficient, “burn in” free organic solar cell employing a nonfullerene electron acceptor.Adv. Mater. 2017; 29: 1701156Crossref Scopus (152) Google Scholar, 34Gasparini N. Salvador M. Strohm S. Heumueller T. Levchuk I. Wadsworth A. Bannock J.H. de Mello J.C. Egelhaaf H.-J. Baran D. et al.Burn-in free nonfullerene-based organic solar cells.Adv. Energy Mater. 2017; 7: 1700770Crossref Scopus (174) Google Scholar In the BHJ solar cell, the actual morphology typically comprises multiple phases depending on the materials used.35Sweetnam S. Graham K.R. Ngongang Ndjawa G.O. Heumüller T. Bartelt J.A. Burke T.M. Li W. You W. Amassian A. McGehee M.D. Characterization of the polymer energy landscape in polymer: fullerene bulk heterojunctions with pure and mixed phases.J. Am. Chem. Soc. 2014; 136: 14078-14088Crossref PubMed Scopus (180) Google Scholar, 36Buchaca-Domingo E. Ferguson A.J. Jamieson F.C. McCarthy-Ward T. Shoaee S. Tumbleston J.R. Reid O.G. Yu L. Madec M.-B. Pfannmöller M. et al.Additive-assisted supramolecular manipulation of polymer: fullerene blend phase morphologies and its influence on photophysical processes.Mater. Horiz. 2014; 1: 270-279Crossref Google Scholar For an amorphous polymer donor and with suppression of the crystallization of the small molecule acceptor (SMA), the phase diagram is asymmetric and there are only two domains: the acceptor-rich small molecule domain that is almost pure in sufficiently immiscible systems, and the donor rich, mixed amorphous domain.37Ye L. Hu H. Ghasemi M. Wang T. Collins B.A. Kim J.H. Jiang K. Carpenter J.H. Li H. Li Z. et al.Quantitative relations between interaction parameter, miscibility and function in organic solar cells.Nat. Mater. 2018; 17: 253-260Crossref PubMed Scopus (432) Google Scholar In addition to these two domains, a semi-crystalline donor based device has an additional pure polymer crystalline domain. The crystallization of the SMA (fullerene or NF-SMA) is usually prevented in fresh devices by quenching the acceptor into an amorphous, vitrified state.15de Zerio A.D. Müller C. Glass forming acceptor alloys for highly efficient and thermally stable ternary organic solar cells.Adv. Energy Mater. 2018; 8: 1702741Crossref Scopus (69) Google Scholar This two- or three-phase morphology must be carefully optimized to maximize the photon absorption, exciton separation, and charge transportation and extraction simultaneously. Such an optimization often creates mixed domains with an unstable composition (Figure 1).22Li N. Perea J.D. Kassar T. Richter M. Heumueller T. Matt G.J. Hou Y. Güldal N.S. Chen H. Chen S. et al.Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing.Nat. Commun. 2017; 8: 14541Crossref PubMed Scopus (263) Google Scholar, 38Liu Y. Zhao J. Li Z. Mu C. Ma W. Hu H. Jiang K. Lin H. Ade H. Yan H. Aggregation and morphology control enables multiple cases of high-efficiency polymer solar cells.Nat. Commun. 2014; 5: 5293Crossref PubMed Scopus (2727) Google Scholar, 39Müller C. On the glass transition of polymer semiconductors and its impact on polymer solar cell stability.Chem. Mater. 2015; 27: 2740-2754Crossref Scopus (179) Google Scholar, 40Ye L. Collins B.A. Jiao X. Zhao J. Yan H. Ade H. Miscibility-function relations in organic solar cells: significance of optimal miscibility in relation to percolation.Adv. Energy Mater. 2018; 8: 1703058Crossref Scopus (194) Google Scholar For crystallizable SMAs, the meta-stable state of the amorphous domains is governed by the binodal composition, also referred to as the miscibility gap.41Rathi P. Huang T.M. Dayal P. Kyu T. Crystalline−amorphous interaction in relation to the phase diagrams of binary polymer blends containing a crystalline constituent.J. Phys. Chem. B. 2008; 112: 6460-6466Crossref PubMed Scopus (37) Google Scholar The thermodynamically favored (stable) state involves SMA crystals, a state described by the liquidus in the phase diagram. This state depletes the mixed domains of SMA relative to the binodal because of the extra chemical potential of the crystals. Please note that we will use the term binodal or miscibility gap and liquidus for simplicity even in cases where the liquid phases have vitrified to an amorphous glass below the glass transition temperature Tg, and the phase boundaries correspond to solid-solid transitions. The binodal or miscibility gap is governed by the miscibility limit of the donor or acceptor materials in the majority phase, which can be parameterized in favorable cases by the effective amorphous-amorphous Flory-Huggins (F-H) interaction parameter χ.42Kouijzer S. Michels J.J. van den Berg M. Gevaerts V.S. Turbiez M. Wienk M.M. Janssen R.A.J. Predicting morphologies of solution processed polymer: fullerene blends.J. Am. Chem. Soc. 2013; 135: 12057-12067Crossref PubMed Scopus (241) Google Scholar, 43Kozub D.R. Vakhshouri K. Orme L.M. Wang C. Hexemer A. Gomez E.D. Polymer crystallization of partially miscible polythiophene/fullerene mixtures controls morphology.Macromolecules. 2011; 44: 5722-5726Crossref Scopus (240) Google Scholar It has been shown recently that the temperature-dependent χ(T) is quantitatively related to the domain purity and fill factor (FF) in a number of systems.37Ye L. Hu H. Ghasemi M. Wang T. Collins B.A. Kim J.H. Jiang K. Carpenter J.H. Li H. Li Z. et al.Quantitative relations between interaction parameter, miscibility and function in organic solar cells.Nat. Mater. 2018; 17: 253-260Crossref PubMed Scopus (432) Google Scholar A relatively high χ is needed for strong-enough phase separation and, thus, high device FF. However, an excessive repulsive molecular interaction between donor and acceptor materials can lead to over-purification of the mixed domains (i.e., with an SMA concentration below the percolation threshold), which would negatively affect device performance predominantly because of charge trapping and mono-molecular recombination.37Ye L. Hu H. Ghasemi M. Wang T. Collins B.A. Kim J.H. Jiang K. Carpenter J.H. Li H. Li Z. et al.Quantitative relations between interaction parameter, miscibility and function in organic solar cells.Nat. Mater. 2018; 17: 253-260Crossref PubMed Scopus (432) Google Scholar, 40Ye L. Collins B.A. Jiao X. Zhao J. Yan H. Ade H. Miscibility-function relations in organic solar cells: significance of optimal miscibility in relation to percolation.Adv. Energy Mater. 2018; 8: 1703058Crossref Scopus (194) Google Scholar, 44Bartelt J.A. Beiley Z.M. Hoke E.T. Mateker W.R. Douglas J.D. Collins B.A. Tumbleston J.R. Graham K.R. Amassian A. Ade H. et al.The importance of fullerene percolation in the mixed regions of polymer-fullerene bulk heterojunction solar cells.Adv. Energy Mater. 2013; 3: 364-374Crossref Scopus (406) Google Scholar, 45Ye L. Li S. Liu X. Zhang X. Ghasemi M. Xiong Y. Hou J. Ade H. Quenching to the percolation threshold in organic solar cells.Joule. 2018; 3: 443-458Abstract Full Text Full Text PDF Scopus (142) Google Scholar Schematics of the possible scenarios of morphology evolution in an upper critical solution temperature (UCST) polymer:SMA blend with an amorphous donor and crystallizable SMA with a low and an optimal miscibility are illustrated in Figure 1. Severe burn-in degradation can be expected when the optimal morphology is quenched near the percolation threshold and is far from the miscibility gap, referred to as a “low-” or “hypo-miscibility” system (Figure 1A). On the other hand, a device with a miscibility gap close to the percolation threshold (Figure 1B) during the normal device operation conditions is referred to as “optimal miscibility” and is expected to exhibit a relatively stable morphology and thus lower or slower burn-in degradation. Hyper-miscibility systems typically yield low performance37Ye L. Hu H. Ghasemi M. Wang T. Collins B.A. Kim J.H. Jiang K. Carpenter J.H. Li H. Li Z. et al.Quantitative relations between interaction parameter, miscibility and function in organic solar cells.Nat. Mater. 2018; 17: 253-260Crossref PubMed Scopus (432) Google Scholar and are not further considered. One example of a hypo-miscibility, high-performing polymer:SMA blend system (as illustrated in Figure 1A) is PffBT4T-2OD:PC71BM, with a PC71BM meta-stable equilibrium concentration in the mixed domains well below the percolation threshold.38Liu Y. Zhao J. Li Z. Mu C. Ma W. Hu H. Jiang K. Lin H. Ade H. Yan H. Aggregation and morphology control enables multiple cases of high-efficiency polymer solar cells.Nat. Commun. 2014; 5: 5293Crossref PubMed Scopus (2727) Google Scholar, 40Ye L. Collins B.A. Jiao X. Zhao J. Yan H. Ade H. Miscibility-function relations in organic solar cells: significance of optimal miscibility in relation to percolation.Adv. Energy Mater. 2018; 8: 1703058Crossref Scopus (194) Google Scholar Consequently, abnormally strong burn-in degradation is observed in PffBT4T-2OD:PC71BM solar cells as [6,6]-phenyl C61 or C71 butyric acid methyl ester (PCBM) readily diffuses even at RT.22Li N. Perea J.D. Kassar T. Richter M. Heumueller T. Matt G.J. Hou Y. Güldal N.S. Chen H. Chen S. et al.Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing.Nat. Commun. 2017; 8: 14541Crossref PubMed Scopus (263) Google Scholar In contrast, PCDTBT:PC71BM is a near optimally miscible system, which should provide improved shelf stability with regard to demixing of the mixed domain when compared to PffBT4T-2OD:PC71BM.37Ye L. Hu H. Ghasemi M. Wang T. Collins B.A. Kim J.H. Jiang K. Carpenter J.H. Li H. Li Z. et al.Quantitative relations between interaction parameter, miscibility and function in organic solar cells.Nat. Mater. 2018; 17: 253-260Crossref PubMed Scopus (432) Google Scholar However, PCDTBT:PC61BM blends, similar to other fullerene-based OSCs, are prone to crystallization of the fullerene, and although these blends are thermodynamically stabilized against amorphous demixing, they are only kinetically stabilized against degradation by crystallization, the second main morphological degradation pathway.46Li Z. Ho Chiu K. Shahid Ashraf R. Fearn S. Dattani R. Cheng Wong H. Tan C.H. Wu J. Cabral J.T. Durrant J.R. Toward improved lifetimes of organic solar cells under thermal stress: substrate-dependent morphological stability of PCDTBT: PCBM films and devices.Sci. Rep. 2015; 5: 15149Crossref PubMed Scopus (46) Google Scholar, 47Wong H.C. Li Z. Tan C.H. Zhong H. Huang Z. Bronstein H. McCulloch I. Cabral J.T. Durrant J.R. Morphological stability and performance of polymer–fullerene solar cells under thermal stress: the impact of photoinduced PC60BM oligomerization.ACS Nano. 2014; 8: 1297-1308Crossref PubMed Scopus (115) Google Scholar It is known that thermal annealing can boost the efficiency of many OSCs; however, heating may accelerate the transition of the morphology from the meta-stable miscibility gap to the liquidus or directly and simultaneously lead to crystallization failure as a result of nucleation or growth of SMA crystals.15de Zerio A.D. Müller C. Glass forming acceptor alloys for highly efficient and thermally stable ternary organic solar cells.Adv. Energy Mater. 2018; 8: 1702741Crossref Scopus (69) Google Scholar The propensity for this transition to occur will depend on Tg, which is an indicator of the degree of vitrification at RT. Conceptually, there are three main classes of systems for crystallizable NF-SMA: class I systems that are unstable as a result of demixing and crystallization (low Tg case in Figure 1A), class II systems that have meta-stable mixed domains but can crystallize (low Tg case in Figure 1B), and class III systems that are kinetically stabilized irrespective of whether they are meta-stable or not (high Tg cases). Class III can be subdivided into class IIIa when a hypo-miscibility system is vitrified and class IIIb when an optimal miscibility, meta-stable system is vitrified. In Figure 1, we measure the phase diagrams of NF-SMA OSC systems for the first time at least partially and delineate thermodynamic drivers and kinetic factors for stability in the three main classes of NF-SMA OSC systems delineated above. We select and utilize the well-known, prototypical NF-SMAs (i.e., EH-IDTBR and ITIC) selectively blended with the prototypical semiconductor polymers P3HT (semi-crystalline, ductile) and FTAZ (amorphous, ductile) to yield three different donor-acceptor blend-based systems in this study (P3HT:EH-IDTBR, FTAZ:EH-IDTBR, and FTAZ:ITIC) that systematically exemplify the characteristics of the different scenarios. We determine their device morphology and operational shelf-stability for variable processing conditions. We also investigate the thermodynamic drivers and kinetic factors of a previously reported relatively stable NF-SMA system based on another prototypical amorphous donor, namely PTB7-Th:EH-IDTBR,19Baran D. Gasparini N. Wadsworth A. Tan C.H. Wehbe N. Song X. Hamid Z. Zhang W. Neophytou M. Kirchartz T. et al.Robust nonfullerene solar cells approaching unity external quantum efficiency enabled by suppression of geminate recombination.Nat. Commun. 2018; 9: 2059Crossref PubMed Scopus (134) Google Scholar as a comparison (the 4th system). It is found that P3HT:EH-IDTBR-based OSCs suffer from severe burn-in degradation in both as-cast and annealed samples. The severe efficiency loss of P3HT:EH-IDTBR devices is more pronounced in annealed devices compared to as-cast devices, even when these films are only briefly annealed at moderately elevated temperatures (120°C for 10 min). Even short periods of annealing are sufficient to nucleate crystals of the NF-SMA, which then assert their presence and negative influence over time. On the other hand, as-cast blend films based on FTAZ:EH-IDTBR exhibit low burn-in loss, whereas strong burn-in degradation occurs readily in annealed FTAZ:EH-IDTBR devices. In contrast, by substituting EH-IDTBR with ITIC, the FTAZ:ITIC-based systems provide OSCs with reduced burn-in degradation in both as-cast and low temperature annealed (120°C) devices, but with severe burn-in in high T annealed (180°C) devices. We determine χ(T) for P3HT:EH-IDTBR, the liquidus for FTAZ:EH-IDTBR, and FTAZ:ITIC-based systems, and the binodal at 110°C and 100°C for PTB7-Th:EH-IDTBR. In addition, we estimated RT diffusion coefficients of 1.7 × 10−17, 2.0 × 10−18, and 4 × 10−20 cm2/s for EH-IDTBR in P3HT, FTAZ, and PTB7-Th, respectively, and analyzed device stability in light of the thermodynamic and kinetic knowledge gained. The diffusion coefficient of EH-IDTBR in P3HT- and FTAZ-based systems is sufficiently high to enable demixing and crystallization burn-in after low T annealing or even in as-cast devices. The more robust morphology of PTB7-Th:EH-IDTBR devices is attributed to the smaller diffusion coefficient of EH-IDTBR in PTB7-Th. These results indicate that NF-SMA OSCs can be stabilized by employing an NF-SMA with a high Tg or a polymer with lower ductility that suppresses the crystallization of the NF-SMA. In order for NF-SMA-based OSCs to be a viable technology, the quenched morphology that gives high performance has to be stabilized against demixing or crystallization by a high degree of vitrification with low diffusion (∼1 × 10−22 cm2/s) or systems have to be meta-stable with a mixed composition near the percolation threshold, and the crystallization of the NF-SMA has to be suppressed or intr}, number={5}, journal={JOULE}, author={Ghasemi, Masoud and Hu, Huawei and Peng, Zhengxing and Rech, Jeromy James and Angunawela, Indunil and Carpenter, Joshua H. and Stuard, Samuel J. and Wadsworth, Andrew and McCulloch, Iain and You, Wei and et al.}, year={2019}, month={May}, pages={1328–1348} }
 @article{yao_li_hu_chow_chen_zhao_li_carpenter_lai_yang_et al._2018, title={A Facile Method to Fine-Tune Polymer Aggregation Properties and Blend Morphology of Polymer Solar Cells Using Donor Polymers with Randomly Distributed Alkyl Chains}, volume={8}, ISSN={["1614-6840"]}, DOI={10.1002/aenm.201701895}, abstractNote={Abstract The device performance of polymer solar cells (PSCs) is strongly dependent on the blend morphology. One of the strategies for improving PSC performance is side‐chain engineering, which plays an important role in controlling the aggregation properties of the polymers and thus the domain crystallinity/purity of the donor–acceptor blends. In particular, for a family of high‐performance donor polymers with strong temperature‐dependent aggregation properties, the device performances are very sensitive to the size of alkyl chains, and the best device performance can only be achieved with an optimized odd‐numbered alkyl chain. However, the synthetic route of odd‐numbered alkyl chains is costly and complicated, which makes it difficult for large‐scale synthesis. Here, this study presents a facile method to optimize the aggregation properties and blend morphology by employing donor polymers with a mixture of two even‐numbered, randomly distributed alkyl chains. In a model polymer system, this study suggests that the structural and electronic properties of the random polymers comprising a mixture of 2‐octyldodecyl and 2‐decyltetradecyl alkyl chains can be systematically tuned by varying the mixing ratio, and a high power conversion efficiency (11.1%) can be achieved. This approach promotes the scalability of donor polymers and thus facilitates the commercialization of PSCs.}, number={6}, journal={ADVANCED ENERGY MATERIALS}, author={Yao, Huatong and Li, Yunke and Hu, Huawei and Chow, Philip C. Y. and Chen, Shangshang and Zhao, Jingbo and Li, Zhengke and Carpenter, Joshua H. and Lai, Joshua Yuk Lin and Yang, Guofang and et al.}, year={2018}, month={Feb} }
 @article{hu_jiang_chow_ye_zhang_li_carpenter_ade_yan_2018, title={Influence of Donor Polymer on the Molecular Ordering of Small Molecular Acceptors in Nonfullerene Polymer Solar Cells}, volume={8}, ISSN={["1614-6840"]}, url={https://publons.com/wos-op/publon/7528287/}, DOI={10.1002/aenm.201701674}, abstractNote={Abstract Nonfullerene polymer solar cells (PSCs) based on polymer donors and nonfullerene small molecular acceptors (SMAs) have recently attracted considerable attention. Although much of the progress is driven by the development of novel SMAs, the donor polymer also plays an important role in achieving efficient nonfullerene PSCs. However, it is far from clear how the polymer donor choice influences the morphology and performance of the SMAs and the nonfullerene blends. In addition, it is challenging to carry out quantitative analysis of the morphology of polymer:SMA blends, due to the low material contrast and overlapping scattering features of the π–π stacking between the two organic components. Here, a series of nonfullerene blends is studied based on ITIC‐Th blended with five different donor polymers. Through quantitative morphology analysis, the (010) coherence length of the SMA is characterized and a positive correlation between the coherence length of the SMA and the device fill factor (FF) is established. The study reveals that the donor polymer can significantly change the molecular ordering of the SMA and thus improve the electron mobility and domain purity of the blend, which has an overall positive effect that leads to the enhanced device FF for nonfullerene PSCs.}, number={5}, journal={ADVANCED ENERGY MATERIALS}, author={Hu, Huawei and Jiang, Kui and Chow, Philip C. Y. and Ye, Long and Zhang, Guangye and Li, Zhengke and Carpenter, Joshua H. and Ade, Harald and Yan, He}, year={2018}, month={Feb} }
 @article{li_mangalore_zhao_carpenter_yan_ade_yan_muellen_blom_pisula_et al._2018, title={Integrated circuits based on conjugated polymer monolayer}, volume={9}, ISSN={["2041-1723"]}, DOI={10.1038/s41467-017-02805-5}, abstractNote={Abstract It is still a great challenge to fabricate conjugated polymer monolayer field-effect transistors (PoM-FETs) due to intricate crystallization and film formation of conjugated polymers. Here we demonstrate PoM-FETs based on a single monolayer of a conjugated polymer. The resulting PoM-FETs are highly reproducible and exhibit charge carrier mobilities reaching 3 cm 2 V −1 s −1 . The high performance is attributed to the strong interactions of the polymer chains present already in solution leading to pronounced edge-on packing and well-defined microstructure in the monolayer. The high reproducibility enables the integration of discrete unipolar PoM-FETs into inverters and ring oscillators. Real logic functionality has been demonstrated by constructing a 15-bit code generator in which hundreds of self-assembled PoM-FETs are addressed simultaneously. Our results provide the state-of-the-art example of integrated circuits based on a conjugated polymer monolayer, opening prospective pathways for bottom-up organic electronics.}, journal={NATURE COMMUNICATIONS}, author={Li, Mengmeng and Mangalore, Deepthi Kamath and Zhao, Jingbo and Carpenter, Joshua H. and Yan, Hongping and Ade, Harald and Yan, He and Muellen, Klaus and Blom, Paul W. M. and Pisula, Wojciech and et al.}, year={2018}, month={Jan} }
 @article{ye_hu_ghasemi_wang_collins_kim_jiang_carpenter_li_li_et al._2018, title={Quantitative relations between interaction parameter, miscibility and function in organic solar cells}, volume={17}, ISSN={["1476-4660"]}, url={https://doi.org/10.1038/s41563-017-0005-1}, DOI={10.1038/s41563-017-0005-1}, number={3}, journal={NATURE MATERIALS}, publisher={Springer Nature}, author={Ye, Long and Hu, Huawei and Ghasemi, Masoud and Wang, Tonghui and Collins, Brian A. and Kim, Joo-Hyun and Jiang, Kui and Carpenter, Joshua H. and Li, Hong and Li, Zhengke and et al.}, year={2018}, month={Mar}, pages={253–260} }
 @article{gautam_younts_carpenter_ade_gundogdu_2018, title={The Role of FRET in Non-Fullerene Organic Solar Cells: Implications for Molecular Design}, volume={122}, ISSN={["1089-5639"]}, url={https://doi.org/10.1021/acs.jpca.7b12807}, DOI={10.1021/acs.jpca.7b12807}, abstractNote={Non-fullerene acceptors (NFAs) have been demonstrated to be promising candidates for highly efficient organic photovoltaic (OPV) devices. The tunability of absorption characteristics of NFAs can be used to make OPVs with complementary donor–acceptor absorption to cover a broad range of the solar spectrum. However, both charge transfer from donor to acceptor moieties and energy (energy) transfer from high-bandgap to low-bandgap materials are possible in such structures. Here, we show that when charge transfer and exciton transfer processes are both present, the coexistence of excitons in both domains can cause a loss mechanism. Charge separation of excitons in a low-bandgap material is hindered due to exciton population in the larger bandgap acceptor domains. Our results further show that excitons in low-bandgap material should have a relatively long lifetime compared to the transfer time of excitons from higher bandgap material in order to contribute to the charge separation. These observations provide significant guidance for design and development of new materials in OPV applications.}, number={15}, journal={JOURNAL OF PHYSICAL CHEMISTRY A}, publisher={American Chemical Society (ACS)}, author={Gautam, Bhoj R. and Younts, Robert and Carpenter, Joshua and Ade, Harald and Gundogdu, Kenan}, year={2018}, month={Apr}, pages={3764–3771} }
 @article{zhong_ye_chen_jo_chueh_carpenter_ade_jen_2017, title={A regioregular conjugated polymer for high performance thick-film organic solar cells without processing additive}, volume={5}, ISSN={["2050-7496"]}, url={https://doi.org/10.1039/C7TA02391J}, DOI={10.1039/c7ta02391j}, abstractNote={Regioregular PTB7-Th with pre-designated repeat units achieves over 10% efficiency in thick-film solar cells without the assistance of a solvent additive.}, number={21}, journal={JOURNAL OF MATERIALS CHEMISTRY A}, publisher={Royal Society of Chemistry (RSC)}, author={Zhong, Hongliang and Ye, Long and Chen, Jung-Yao and Jo, Sae Byeok and Chueh, Chu-Chen and Carpenter, Joshua H. and Ade, Harald and Jen, Alex K. -Y.}, year={2017}, month={Jun}, pages={10517–10525} }
 @article{yu_chung_shewmon_ho_carpenter_larrabee_sun_jones_ade_o'connor_et al._2017, title={Flexible inorganic ferroelectric thin films for nonvolatile memory devices}, volume={27}, number={21}, journal={Advanced Functional Materials}, author={Yu, H. and Chung, C. C. and Shewmon, N. and Ho, S. and Carpenter, J. H. and Larrabee, R. and Sun, T. L. and Jones, J. L. and Ade, H. and O'Connor, B. T. and et al.}, year={2017} }
 @article{ye_zhao_li_mukherjee_carpenter_awartani_jiao_hou_ade_2017, title={High-Efficiency Nonfullerene Organic Solar Cells: Critical Factors that Affect Complex Multi-Length Scale Morphology and Device Performance}, volume={7}, ISSN={["1614-6840"]}, url={https://publons.com/wos-op/publon/5290907/}, DOI={10.1002/aenm.201602000}, abstractNote={Organic solar cells (OSCs) made of donor/acceptor bulk-heterojunction active layers have been of widespread interest in converting sunlight to electricity. Characterizing of the complex morphology at multiple length scales of polymer:nonfullerene small molecular acceptor (SMA) systems remains largely unexplored. Through detailed characterizations (hard/soft X-ray scattering) of the record-efficiency polymer:SMA system with a close analog, quantitative morphological parameters are related to the device performance parameters and fundamental morphology–performance relationships that explain why additive use and thermal annealing are needed for optimized performance are established. A linear correlation between the average purity variations at small length scale (≈10 nm) and photovoltaic device characteristics across all processing protocols is observed in ≈12%-efficiency polymer:SMA systems. In addition, molecular interactions as reflected by the estimated Flory–Huggins interaction parameters are used to provide context of the room temperature morphology results. Comparison with results from annealed devices suggests that the two SMA systems compared show upper and lower critical solution temperature behavior, respectively. The in-depth understanding of the complex multilength scale nonfullerene OSC morphology may guide the device optimization and new materials development and indicates that thermodynamic properties of materials systems should be studied in more detail to aid in designing optimized protocols efficiently.}, number={7}, journal={ADVANCED ENERGY MATERIALS}, author={Ye, Long and Zhao, Wenchao and Li, Sunsun and Mukherjee, Subhrangsu and Carpenter, Joshua H. and Awartani, Omar and Jiao, Xuechen and Hou, Jianhui and Ade, Harald}, year={2017}, month={Apr} }
 @article{di pietro_erdmann_carpenter_wang_shivhare_formanek_heintze_voit_neher_ade_et al._2017, title={Synthesis of High-Crystallinity DPP Polymers with Balanced Electron and Hole Mobility}, volume={29}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.7b04423}, abstractNote={We review the Stille coupling synthesis of P(DPP2OD-T) (Poly[[2,5-di(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-3,6-diyl]-alt-[2,2′:5′,2″-terthiophene-5,5″-diyl]]) and show that high-quality, high molecular weight polymer chains are already obtained after as little as 15 min of reaction time. The results of UV–vis spectroscopy, grazing incidence wide-angle X-ray scattering (GIWAXS), and atomic force microscopy show that longer reaction times are unnecessary and do not produce any improvement in film quality. We achieve the best charge transport properties with polymer batches obtained from short reaction times and demonstrate that the catalyst washing step is responsible for the introduction of charge-trapping sites for both holes and electrons. These trap sites decrease the charge injection efficiency, strongly reducing the measured currents. The careful tuning of the synthesis allows us to reduce the reaction time by more than 100 times, achieving a more environmentally friendly, less costly ...}, number={23}, journal={CHEMISTRY OF MATERIALS}, author={Di Pietro, Riccardo and Erdmann, Tim and Carpenter, Joshua H. and Wang, Naixiang and Shivhare, Rishi Ramdas and Formanek, Petr and Heintze, Cornelia and Voit, Brigitte and Neher, Dieter and Ade, Harald and et al.}, year={2017}, month={Dec}, pages={10220–10232} }
 @article{di pietro_nasrallah_carpenter_gann_koelln_thomsen_venkateshvaran_o'hara_sadhanala_chabinyc_et al._2016, title={Coulomb Enhanced Charge Transport in Semicrystalline Polymer Semiconductors}, volume={26}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201602080}, abstractNote={Polymer semiconductors provide unique possibilities and flexibility in tailoring their optoelectronic properties to match specific application demands. The recent development of semicrystalline polymers with strongly improved charge transport properties forces a review of the current understanding of the charge transport mechanisms and how they relate to the polymer's chemical and structural properties. Here, the charge density dependence of field effect mobility in semicrystalline polymer semiconductors is studied. A simultaneous increase in mobility and its charge density dependence, directly correlated to the increase in average crystallite size of the polymer film, is observed. Further evidence from charge accumulation spectroscopy shows that charges accumulate in the crystalline regions of the polymer film and that the increase in crystallite size affects the average electronic orbitals delocalization. These results clearly point to an effect that is not caused by energetic disorder. It is instead shown that the inclusion of short range coulomb repulsion between charge carriers on nanoscale crystalline domains allows describing the observed mobility dependence in agreement with the structural and optical characterization. The conclusions that are extracted extend beyond pure transistor characterization and can provide new insights into charge carrier transport for regimes and timescales that are relevant to other optoelectronic devices.}, number={44}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Di Pietro, Riccardo and Nasrallah, Iyad and Carpenter, Joshua and Gann, Eliot and Koelln, Lisa Sophie and Thomsen, Lars and Venkateshvaran, Deepak and O'Hara, Kathryn and Sadhanala, Aditya and Chabinyc, Michael and et al.}, year={2016}, month={Nov}, pages={8011–8022} }
 @article{huang_carpenter_li_yu_ade_jen_2016, title={Highly Efficient Organic Solar Cells with Improved Vertical Donor-Acceptor Compositional Gradient Via an Inverted Off-Center Spinning Method}, volume={28}, ISSN={["1521-4095"]}, DOI={10.1002/adma.201504014}, abstractNote={A novel, yet simple solution fabrication technique to address the trade-off between photocurrent and fill factor in thick bulk heterojunction organic solar cells is described. The inverted off-center spinning technique promotes a vertical gradient of the donor-acceptor phase-separated morphology, enabling devices with near 100% internal quantum efficiency and a high power conversion efficiency of 10.95%.}, number={5}, journal={ADVANCED MATERIALS}, author={Huang, Jiang and Carpenter, Joshua H. and Li, Chang-Zhi and Yu, Jun-Sheng and Ade, Harald and Jen, Alex K. -Y.}, year={2016}, month={Feb}, pages={967–974} }
 @article{zhong_wu_li_carpenter_chueh_chen_ade_jen_2016, title={Rigidifying Nonplanar Perylene Diimides by Ring Fusion Toward Geometry-Tunable Acceptors for High-Performance Fullerene-Free Solar Cells}, volume={28}, ISSN={["1521-4095"]}, DOI={10.1002/adma.201504120}, abstractNote={Rigid fused perylene diimide (PDI) dimers bridged with heterocycles exhibit superior photovoltaic performance compared to their unfused semiflexible analogues. Changing the chalcogen atoms in the aromatic bridges gradually increases the twist angles between the two PDI planes, leading to a varied morphology in which the one bridged by thiophene achieves a balance and shows the best efficiency of 6.72%.}, number={5}, journal={ADVANCED MATERIALS}, author={Zhong, Hongliang and Wu, Chen-Hao and Li, Chang-Zhi and Carpenter, Joshua and Chueh, Chu-Chen and Chen, Jung-Yao and Ade, Harald and Jen, Alex K. -Y.}, year={2016}, month={Feb}, pages={951–958} }
 @article{li_lin_jiang_carpenter_li_liu_hu_zhao_ma_ade_et al._2015, title={Dramatic performance enhancement for large bandgap thick-film polymer solar cells introduced by a difluorinated donor unit}, volume={15}, ISSN={["2211-3282"]}, DOI={10.1016/j.nanoen.2015.05.016}, abstractNote={We report a large bandgap (1.9 eV) donor–acceptor copolymer (named PffT2-FTAZ) that enables polymer solar cells with a high power conversion efficiency of 7.8%. An important structural feature of the PffT2-FTAZ polymer is a difluorinated donor unit (3,3′-difluoro-2,2′-bithiophene, or, ffT2) that introduces several surprising and/or beneficial effects. By comparing PffT2-FTAZ with the analog polymer (PT2-FTAZ) without fluorination on the bithiophene donor unit, it is found that the ffT2 unit effectively lowers the HOMO and LUMO energy levels of the polymer and slightly reduces optical bandgap. It also introduces strong interchain aggregation for the polymer in solution, which leads to a highly crystalline polymer film and reasonably high hole transport mobility. On the other hand, the PffT2-FTAZ: fullerene blend still exhibits a reasonably small polymer domain size suitable for polymer solar cell operation. All these positive factors combined leads to dramatically enhanced performance for the polymer solar cells with the power conversion efficiency increasing from 2.8% for PT2-FTAZ to 7.8% for f PffT2-FTAZ. The high PSC performance of PffT2-FTAZ makes it a promising candidate for high efficiency tandem PSCs.}, journal={NANO ENERGY}, author={Li, Zhengke and Lin, Haoran and Jiang, Kui and Carpenter, Joshua and Li, Yunke and Liu, Yuhang and Hu, Huawei and Zhao, Jingbo and Ma, Wei and Ade, Harald and et al.}, year={2015}, month={Jul}, pages={607–615} }
 @article{zhong_li_carpenter_ade_jen_2015, title={Influence of Regio- and Chemoselectivity on the Properties of Fluoro-Substituted Thienothiophene and Benzodithiophene Copolymers}, volume={137}, ISSN={["1520-5126"]}, DOI={10.1021/jacs.5b04209}, abstractNote={By studying the regio- and chemoselectivity of fluoro-substituted thienothiophene and benzodithiophene copolymers, we found polymers made from conventional one-pot polycondensation reaction consist of two distinctly different segments with a ratio of 0.36/0.64. Through further comparative studies of neat regioregular polymers based on each individual segment, we have identified the specific segment that contributes to the superior absorption, packing order, and charge mobility in the corresponding polymers. The unique structure–property relationships are the result of cooperative molecular arrangements of the key segment and noncovalent interaction between the fluoro group and the aromatic proton on the thiophene side-chain of the polymers.}, number={24}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Zhong, Hongliang and Li, Chang-Zhi and Carpenter, Joshua and Ade, Harald and Jen, Alex K. -Y.}, year={2015}, month={Jun}, pages={7616–7619} }
 @article{ma_yang_jiang_carpenter_wu_meng_mcafee_zhao_zhu_wang_et al._2015, title={Influence of processing parameters and molecular weight on the morphology and properties of high-performance PffBT4T-2OD:PC71BM organic solar cells}, volume={5}, DOI={10.1002/aenm.201570126}, abstractNote={The detailed morphology of high efficiency polymer (PffBT4T-2OD) based organic solar cells is investigated by Wei Ma, Harald Ade, He Yan and co-workers in article number 1501400. It is found that the median domain sizes of PffBT4T-2OD:PC71BM blends processed at different temperatures/spin rates are nearly identical, while the average domain purity and the molecular orientation relative to polymer:fullerene interfaces can be significantly changed by the processing conditions.}, number={23}, journal={Advanced Energy Materials}, author={Ma, W. and Yang, G. F. and Jiang, K. and Carpenter, J. H. and Wu, Y. and Meng, X. Y. and McAfee, T. and Zhao, J. B. and Zhu, C. H. and Wang, C. and et al.}, year={2015} }
 @article{karpusenko_carpenter_zhou_lim_pan_riehn_2012, title={Fluctuation modes of nanoconfined DNA}, volume={111}, number={2}, journal={Journal of Applied Physics}, author={Karpusenko, A. and Carpenter, J. H. and Zhou, C. D. and Lim, S. F. and Pan, J. H. and Riehn, R.}, year={2012} }
 @article{carpenter_karpusenko_pan_lim_riehn_2011, title={Density fluctuations dispersion relationship for a polymer confined to a nanotube}, volume={98}, number={25}, journal={Applied Physics Letters}, author={Carpenter, J. H. and Karpusenko, A. and Pan, J. H. and Lim, S. F. and Riehn, R.}, year={2011} }